Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$168.83	12.838%	$190.5044	$190.50	$190.50	$190.50
Purchase #2	$134.25	7.456%	$144.2597	$144.26	$144.25	$144.30
Purchase #3	$245.64	12.535%	$276.431	$276.43	$276.45	$276.40
Purchase #4	$120.27	6.871%	$128.5338	$128.53	$128.55	$128.50
Purchase #5	$217.40	3.326%	$224.6307	$224.63	$224.65	$224.60
Purchase #6	$220.62	8.160%	$238.6226	$238.62	$238.60	$238.60
Purchase #7	$57.41	6.867%	$61.3523	$61.35	$61.35	$61.40
7 purchase totals =	$1,164.42		$1,264.3345	$1,264.32	$1,264.35	$1,264.30